I. Field of the Invention
The present invention relates generally to gear boxes with means for adjusting the rotary speed with which its output shaft is driven and, more particularly, to a gear box having a planetary gear mechanism in which the planet gear carrier itself forms a gear, to drive a second stage gear, and wherein the gear box includes hydraulically actuated clutches driven by a hydraulic amplifier.
II. Description of the Prior Art
There are many known forms of gear boxes for drive trains connecting power from a motor such as an internal combustion engine to drive wheels of a vehicle, an airplane propeller, industrial machines and the like. However, reduction of the size and weight of the power train used in an aircraft is particularly important to the optimum efficiency and performance of the aircraft. As a result, many known drive trains are inappropriate for use in aircraft.
Gear boxes often provide not only speed reduction, but also variability of the speed at which the output shaft is driven. One known form of a gear box for generating the desired output speed comprises a planetary gear system. In such a system, a plurality of planet gears are engaged between an outer ring gear and a sun gear, and the axes of the planet gears are tied together by a carrier or cage. The difference between the speeds at which the carrier and the ring gear rotate is used to advantage in varying the speed of the output shaft of the gear box. Clutches are used to selectively lock one gear set with respect to another to vary the rotary output speed ratio.
In addition, since the numerous gears in a planetary system must be lubricated, a pressurized flow of lubricant is often used to distribute the lubrication throughout the gear box housing. Typically, the pressure is generated by a high pressure pump which is driven by the motor used to drive the gear box. A separate scavenge pump circulates lubricant from the gear box back to a reservoir. The scavenge pump further increases the weight and size of the drive train.
Another feature which inhibits minimizing the size and weight of a gear box is the fact that the planet gear carrier is also formed separately from the driving components of the gear system and thus, substantially increases the length and weight of the planetary gear arrangement.
In addition, when clutches are used to selectively lock specific gears to vary the rotary output speed ratio, the clutch actuating system also adds substantially to the bulk and size of the gear box housing. Typically, hydraulically actuated clutches are used, and thus require a source of highly pressurized fluid to actuate the clutches. High pressure fluid is usually generated by a separate pump which is driven continuously by the motor. This arrangement further reduces the power available to operate the gear box, and adds to the weight and size of the drive train.